Related Clues:

• Ref. wd.
• It's added to an env.
• Env. add-in
• "Look inside" abbr.
• Stamped return env., for example
• Placed inside: abbr.
• Something inside an env.
• Bus. letter abbr.
• SASE, for one
• 125 Across, e.g.
• End-of-letter letters
• Abbr. on a cover letter
• 25 Across, for one: Abbr.
• SASE, e.g
• Envelope abbr